In conventional electrophotography processes, "ghosting" is a recognized phenomenon. Ghosting results when both the freshly made latent image and at least a portion of a previously made different latent image are concurrently developed on the same surface giving the toned surface a sort of double exposure appearance. Conventionally, ghosting is avoided or minimized by an optical erase or process control procedures in which either the charging voltage (termed V.sub.o) is suitably chosen, or the exposure conditions are appropriately adjusted, or both. When, during imaging, there is neither runaway dark decay nor a large toe rise and ghost production is avoided in a previously charged and exposed photoconductor element, the element is considered to have been fully regenerated.
In certain situations, such as when complex images are generated on certain photoconductor elements with a laser scan, ghosting can not be corrected by conventional procedures. Based on experimentally derived evidence, it is theorized (and there is no intent herein to be bound by theory) that such uncorrectable ghosting is caused by trapped electrons and trapped holes.
A process and apparatus for regenerating without ghost production so-called "single use" electrophotographic film having low optical density p-type photoconductors is provided by U.S. Pat. No. 4,804,602. In accordance with this patent, the film generates mobile holes and trapped electrons throughout the thickness or bulk of the photoconductor film. The regeneration is accomplished by neutralizing the trapped electrons in the photoconductor film by recombination with mobile holes using suitable reverse charging. Such holes were photogenerated to the rear of the trapped electrons or injected from a conductive substrate and allowed to drift to, and recombine with, the trapped electrons. In the practice of such invention, an overall optical erase is used in combination with reverse charging. An optical erase is employed so that no unexposed film areas exist during such reverse charging, thereby avoiding photogeneration or injection of holes in areas of the film where there were no trapped electrons.
In the so-called NP electrophotographic process, a series of charges, and a combination of a simultaneous charge and image exposure are used, followed by an overall exposure or another charge, to produce an image over (upon) an insulating, or dielectric, layer. Thus, the field variation is over the insulator, not the photoconductor. Regeneration procedures for the NP process involve removing the differential field from the insulating layer, not the photoconductor. In these regeneration procedures, an optical erase, or overall exposure, usually in combination with a charge is generally used.
So far as now known, effective procedures for accomplishing photoconductor element regeneration and avoiding ghost production without using optical erase, or overall exposure, have not previously been known. Also, specialized photoconductor element structures, and procedures adapted for use therewith, which accomplish regeneration and avoid ghosting, have not previously been known.